1. Field of the Invention
The present invention relates generally to systems for facilitating the extraction of natural gas deposits from underground geologic formations. The present invention relates more specifically to ball sealer devices commonly known as “frac-balls” that are generally spherical objects that are injected into a well to close off portions of the well to allow pressure to build up and cause fracturing in a target section of the geologic formation.
2. Description of the Related Art
Hydraulic fracturing, commonly referred to as “fracking”, is the process of creating small cracks, or fractures, in underground geological formations to allow natural gas to flow into the wellbore and to the surface where the gas is collected and distributed. Variables such as the permeability and porosity of the surrounding rock formations and the thickness of the targeted shale formations are studied by geoscientists before the fracking process is conducted. The result is a highly sophisticated and carefully engineered process that creates a network of fractures that are contained within the boundaries of the targeted deep shale natural gas formation.
During the fracking process, a mixture of water, sand and other chemical additives designed to protect the integrity of the geological formation and enhance production is pumped under high pressure into the shale formation to create small fractures. The mixture is typically about 99.5% water and sand, along with small amounts of special-purpose additives. The newly created fractures are maintained in an open condition by the sand, which allows the natural gas to flow into the wellbore where it is collected at the surface and subsequently delivered to a wide ranging group of consumers.
One of the tools used by some operators of hydraulic fracturing equipment are specially sized “frac-balls” that are injected into a well to block or close off portions of a well to allow pressure to build up and cause the fracturing in a target section of the well. Frac-balls may be made of various materials, including G-10 (or other related phenolic plastics), Torlon® (polyamide-imide or PAI), PEEK (polyether ether ketone), and other high-temperature thermosets or thermoplastics. Typically, the material selected is based upon the operators' experience and the chemistry and temperatures within the well.
Frac-ball sizes are selected specifically to fit within the well-bore or sliding sleeves which vary in diameter as the well sections progress from upper to lower (or end) sections. One popular method for creating multiple fractures in a wellbore is the use of fracturing ports & sliding sleeves. Open hole packers isolate different sections of the horizontal well. A sliding sleeve is placed between each packer pair and is opened by injecting a properly sized frac-ball inside the borehole. Typically, a completion string is placed inside the well. The completion string includes frac ports and open hole packers spaced to specifications. The spacing between packers may be up to several hundred feet. The packers are actuated by mechanical, hydraulic or chemical mechanisms. In order to activate each sleeve, a properly sized frac-ball is pumped along with a fracturing fluid inside the well. Each ball is smaller than the opening of all of the previous sleeves, but larger than the sleeve it is intended to open. Seating of the frac-ball exerts pressure at the end of the sliding sleeve assembly, causing it to slide and open the frac ports. Once the port is opened, the fluid is diverted into the open hole space outside of the completion assembly, causing the formation to fracture.
At the completion of each fracturing stage, the next larger frac-ball is injected into the well, which opens the next sleeve, and so on, until all of the sleeves are opened and multiple fractures are created in the well. The main advantage of this completion technique is the speed of operation (by activating multiple fractures with a single completion string) which also significantly reduces cost.